This invention relates to a photosensitive stroboscopic or flash lamp which can be used both as a main lamp (herein referred to simply as "the main") and as a slave, and also to a system for optically connecting such a lamp to an underwater camera.
In underwater photography, the use of a flash lamp is nearly indispensable because of the insufficiency of available light. Such a flash lamp for underwater photography (herein referred to simply as "the flash lamp") is usually attached to the tip of an elongated arm member extending from a base plate fastened to the bottom of an underwater camera (herein referred to simply as "the camera") such that its position can be varied for different ways of lighting, depending on the conditions of the situation when the camera is used as well as the effects desired. When it is desired to photograph a target object as accurately as possible or without any shadows, the lamp may be placed in front somewhat above the camera. If some shadows are desired, say, for emphasizing a contrast, the lamp may be placed at a relatively low position on the right-hand or left-hand side of the camera.
With a front lighting, however, the picture tends to be too flat. Similarly, the shadows may become too dark and the picture as a whole may become too somber if the lighting is only from one side. Since the use of only one flash lamp is thus not versatile enough, two flash lamps, including one master and one slave, are often attached to the camera for two-lamp stroboscopic photography. To use such a system for underwater photography, however, the preliminary preparation has been very cumbersome because the functions of the lamps must be preliminarily determined and the lamps must be connected to the camera by means of a water-proof cable for transmission of electrical signals. The basic problem was that the exchange of signals between the camera and the lamp was through electrical connections through a cable. Thus, it was absolutely impossible to set or reset a camera-lamp combination at the very time of underwater photography. Even on a boat, such operations must be carried out inside a cabin where the parts will not be exposed to water. In other words, the setting and resetting of such a system could be done safely only after the user returned to the land.
There are flash lamps of a special kind which may be used as a slave, having a light receiving sensor on the light emitting front surface and being adapted to be used with a master such that when the master emits light, the slave senses it and emits light substantially simultaneously. In such a system, the master and the slave may be considered as being optically connected and since they do not have to be connected by an electrical signal cable, they are convenient for underwater flash photography requiring a plurality of light sources.
With prior art flash lamps adapted to serve both as a main and as a slave, however, the optical link to a camera was not accurate enough. For example, although they could emit light in response to a signal from a camera, they could not reliably respond to a signal from the camera to stop the emission of light. This means that prior art flash lamps were not necessarily capable of providing the right level of exposure required by the camera. When such a lamp was used as the master, furthermore, the exchange of signals with the camera was still through an electrical connection. In other words, prior art lamps were subject to all kinds of limitations when used for underwater photography.